Chemical and stable isotopic composition of thermal waters around Mt. Iwoyama of Kirishima volcanic complex, and their changes associated with volcanic activity

Abstract

Although no fumarolic activity on Mt. Iwoyama of Kirishima volcanic complex has been observed since 2007(Funasaki et al., 2017), new fumaroles have appeared in December 2015.In this study, chemical composition and the stable isotopic ratio of hydrogen and oxygen of thermal waters around Mt. Iwoyama of Kirishima volcanic complex were analyzed and their origin and water quality changes associated with volcanic activity were investigated. Most of them were classified as acid sulfate water and were considered to be originated through the mixing of meteoric water with volcanic fluid basically, but a water collected near the fumarolic area on the summit of Mt. Iwoyama has high chloride concentration and δD and δ¹⁸O values. The changes in water quality and δD and δ¹⁸O values associated with volcanic activity were also recognized.